Vascular graft assemblies and methods for implanting same

ABSTRACT

A graft system is provided that includes either a support ring or a support sleeve that is used in providing transitional support to either an end or a side of a graft or a host vessel. The support ring is provided with a generally cylindrical wall and defining a passageway that is adapted for receiving an end of a vein graft or an end of a host vessel. The support ring has a first end and a second end, with the thickness of the wall being greater at the first end than at the second end. The support sleeve is provided with a first side edge, a second side edge, and an opening. The support sleeve surrounds a side opening of a graft or host vessel so that the opening of the support sleeve is aligned with the side opening of the graft or host vessel. The thickness of the support sleeve is greater at the opening than at the first and second side edges.

RELATED CASES

This is a division of Ser. No. 09/073,743, now U.S. Pat. No. 5,989,287entitled “Vascular Graft Assemblies and Methods for Implanting Same”,filed May 6, 1998, the entire disclosures of which are incorporated bythis reference as though set forth fully herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to vascular grafts and methodsof implantation of vascular grafts, and in particular, to graft systemsor assemblies for use in grafting and methods for deploying these graftsystems in bypass grafting procedures.

2. Description of the Prior Art

Over the past thirty years, a large number of vascular grafts have beensurgically implanted in patients to (i) revascularize blood flow fromdiseased arteries and veins, (ii) to replace the diseased arteries andveins, and (iii) to bypass regions of severe stenosis. These vasculargrafts have been provided in the form of autogenous grafts, syntheticgrafts, or grafts of biological origins (homogeneous or heterogeneous).Synthetic grafts are generally used for mending large arteries, whileautogenous saphenous veins are generally used for arterialreconstruction of smaller vessels (such as in the lower extermities). Inaortocoronary bypass, autogenous vein grafts are typically anastomosedproximally to the ascending aorta and distally to the coronary arterydownstream from the stenosis.

Occlusion of implanted grafts leading to graft failure is a majorproblem encountered in all cases. In general, in the case of coronaryarterial bypass grafts (CABG), the patency rates of human saphenous veingrafts varies, but by ten years, only fifty percent of such implantedgrafts are expected to remain patent, with about half of the patentgrafts suffering from severe atherosclerosis. Unfortunately, the patencyrate is even lower for grafts used in lower-extremity bypass cases.

The causes of such graft failures can be categorized as intrinsic andextrinsic factors. Intrinsic factors involve the adaptations within thegraft wall itself, and intimal hyperplasia and atherosclerosis are twomajor intrinsic factors associated with post-operative failure ofarterial bypass grafts. Extrinsic factors involve physiology related to,but not directly part of, the graft, such as the blood, the arterial bedinto which the graft is placed, and the surgical technique.

In CABG applications, early occlusion (i.e., less than one month fromthe surgical procedure) occurs in about five to fifteen percent of allcases. In fact, graft occlusion within one week of the procedure occursin about seven to eight percent of the cases. These numbers aresignificant, and attempts have been made to minimize the percentage ofearly occlusion cases by (i) utilizing techniques of surgicalpreparation that preserve a nonthrombogenic endothelium, and (ii)providing an optimal anastomosis.

Optimal anastomosis is especially important to the potential patency ofthe graft, but a number of factors make it difficult to achieve. Forexample, the graft opening must be properly sized to prevent kinking atthe anastomotic site. Meticulous (i.e., careful) anastomosis is alsorequired for small anastomosis to obtain good patency. However, theseprocedures may be difficult to accomplish if the vein graft iscollapsed. To address this problem, a pickup forceps is typically usedto hold the vein opening during aortocoronary and peripheral vascularbypass surgery. However, the forceps may cause endothelial injury andcan slip from its position during the anastomosis. Other holding devices(e.g., the Mobin-Uddin vein graft holder) were developed to address thedeficiencies of the forceps, but these devices are still not completelysatisfactory when used for anastomosis because they may still causeinjury to the endothelium, or do not provide satisfactorycircumferential support to the vein graft.

Optimal anastomosis should minimize the occurrence of bleeding. In manycases, bleeding can be a problem after completion of the anastomosis.Although a significant etiologic factor for this bleeding is systemicheparinization or an acquired platelet dysfunction associated withcardiopulmonary bypass, the surgical site may also be a contributingfactor because of suboptimal surgical techniques used during theanastomosis. The proximal anastomosis of an aortocoronary artery bypassgraft is one such potential site. Factors that may contribute tobleeding at this site include the quality of the aorta and implantedsaphenous vein, as well as the anastomotic stitch spacing and tension.However, one factor that is particularly troublesome in some cases isthat the aortotomy is significantly larger in size than the diameter ofthe saphenous vein (i.e., there is a size mismatch). In such cases, thewall of the vein becomes stretched and tensioned at the proximalanastomotic site, as shown in FIG. 3B (which is described in greaterdetail hereinbelow). The size mismatch also results in a tendency forthe anastomotic suture to cut through the vein, resulting in bleeding.Additional stitches placed to control this bleeding may result infurther tearing of the vein, thereby exacerbating the condition so thatthe proximal anastomosis becomes a site of major hemorrhage. In additionto the bleeding problems, a mismatch in the size of the aortotomy andthe saphenous vein graft may cause the vein to flatten at the site ofthe anastomosis, thereby impairing blood flow through the graft.

The optimal way to manage this difficult mismatch situation would be toavoid it by appropriately judging the size of the aortotomy. However, itis very difficult to properly predict how much an anastomosed vein graftwill expand when subject to arterial pressure. Thus, this mismatch inthe size of the aortotomy and the saphenous vein graft will occur inmany cases. If significant bleeding results from such a mismatch orother unsatisfactory vein contour, a number of surgical options areavailable. According to one option, the vein graft can be disconnectedfrom the aortotomy (which is then closed), and the proximal end of thevein graft is refashioned and anastomosed to a more appropriately-sizedaortotomy. According to another option, the vein graft can bedisconnected from the aortotomy (which is then closed), and the vein isanastomosed in end-to-side manner to another saphenous vein graft thathas already been joined to the aorta. Unfortunately, there are potentialproblems with these two surgical options. An aortotomy, especially anoversized one, can be difficult to close hemostatically. In addition, adirect vein-to-vein anastomosis where one of the veins is markedlynarrow may potentially place both grafts at risk for early occlusion. Asa result, a third surgical option is to place a partial-thickness stitchcircumferentially around the aortotomy. A partial-thickness stitch doesnot extend entirely through the wall of the aortotomy, and the stitchhas to be tied with sufficient tension to reduce the circumference ofthe aortotomy but without cutting through the aorta. Unfortunately,partial-thickness stitches may cause the layers that make up theaortotomy to separate (known as delamination).

In addition to minimizing bleeding, an optimal anastomosis should alsoprovide (i) proper anastomotic geometry (e.g., opening, inflow andoutflow tracts) to ensure a smooth rheologic boundary, and (ii) minimalinternal wall stress in connecting vessels or grafts at the anastomoticregion.

Regarding proper anastomotic geometry, it is important to note thatmaterials with different mechanical properties (also known as thiscompliance mismatch), when joined together and placed in a cyclic stresssystem, exhibit different extensibilities. Compliance mismatch can bedefined as the nominal difference in compliance between the blood vesseland a synthetic graft. “Extensibility” describes how much a vessel or agraft expands under arterial pressure. Stress concentrations at or nearthe site of coaptation can result in marked changes of geometry (e.g.,out-of-plane bending, and buckling).

Regarding internal wall stress, it should be noted that compliancemismatches may cause increased stress at the anastomotic sites, as wellas create flow disturbances and turbulence. Suture lines can also causeadditional local compliance mismatches at the connection of the graftand the vessel, and may affect how stress is transmitted to ananastomotic site. It is believed that compliance mismatches at theinterface of the graft and the vessel causes regional hemodynamicdisturbances, which result in turbulent blood flow and shear forces thatare imparted to adjacent flow surfaces. Such flow disruption may lead topara-anastomotic intimal hyperplasia, anastomotic aneurysms, and theacceleration of downstream atherosclerotic change.

Thus, there still remains a need for a graft assembly or system whichpromotes optimal anastomosis, which distributes stresses in an optimalmanner, which is easy to implant, and which generally minimizes oravoids the problems described hereinabove.

SUMMARY OF THE DISCLOSURE

In order to accomplish the objects of the present invention, the presentinvention provides a support ring or a support sleeve that is used inproviding transitional support to either an end or a side of a graft ora host vessel.

According to one embodiment of the present invention, a support ring isprovided having a generally cylindrical wall and defining a passagewaythat is adapted for receiving an end of a vein graft or an end of a hostvessel. The support ring has a first end and a second end, with thethickness of the wall being greater at the first end than at the secondend. In one embodiment, the thickness of the wall gradually decreasesfrom the first end of the support ring to the second end of the supportring. The first end of the support ring is disposed at an angle withrespect to a longitudinal axis that extends through the passageway.

According to another embodiment of the present invention, a supportsleeve is provided having a first side edge, a second side edge, and anopening. The support sleeve surrounds a side opening of a graft or hostvessel so that the opening of the support sleeve is aligned with theside opening of the graft or host vessel. The thickness of the supportsleeve is greater at the opening than at the first and second sideedges. In one embodiment, the thickness of the support sleeve graduallydecreases from the opening of the support sleeve to the first and secondedges thereof. The support sleeve can also be provided in the form of asheet having opposing third and is fourth edges that are stitchedtogether.

The support rings and support sleeves of the present invention can bemade of a material having features or characteristics similar to thoseof an artery so as to facilitate the close matching of the mechanicalproperties or extensibilities. For example, the material can be anelastic material having sufficient stiffness so that it will not expandbeyond a certain limit.

Thus, the support rings and the support sleeve that are used in thegraft systems and methods according to the present invention promoteoptimal anastomosis by providing external circumferential support to theweaker vessel (i.e., either the vein graft or the diseased artery) atthe anastomosis site, and by providing an effective seal for theanastomosis. In addition, the gradually decreasing wall thickness of thesupport rings and the support sleeve provides a gradually tapering orwithdrawing of the support from the anastomotic coaptation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C illustrate a vein graft system and method according to afirst embodiment of the present invention shown, in use to connect anaorta with a coronary artery in an end-to-side manner;

FIG. 2A is a perspective view of the support ring of the graft system ofFIGS. 1A-1C;

FIG. 2B is a longitudinal cross-sectional view of the support ring ofFIG. 2A;

FIG. 3A is a longitudinal cross-sectional view illustrating aconventional end-to-side anastomosis when there is no blood flowtherethrough;

FIG. 3B is a longitudinal cross-sectional view illustrating theend-to-side anastomosis of FIG. 3A when subject to arterial pressure;

FIG. 4A is a longitudinal cross-sectional view illustrating anend-to-side anastomosis accomplished using the graft system and methodof FIGS. 1A-1C when there is no blood flow therethrough;

FIG. 4B is a longitudinal cross-sectional view illustrating theend-to-side anastomosis of FIG. 4A when subject to arterial pressure;

FIGS. 5A-5D illustrate a vein graft system and method according to asecond embodiment of the present invention shown in use to connect twocoronary arteries in an end-to-end manner;

FIG. 6A is a perspective view of the support ring of the graft system ofFIGS. 5A-5D;

FIG. 6B is a longitudinal cross-sectional view of the support ring ofFIG. 6A;

FIGS. 7A-7C illustrate a graft system and method according to a thirdembodiment of the present invention shown in use to connect a vein graftto a coronary artery in a side-to-side manner;

FIG. 8A is a top plan view of a support sheet of the graft system ofFIGS. 7A-7C;

FIG. 8B is a longitudinal cross-sectional view of the support sheet ofFIG. 8A;

FIG. 9 illustrates a graft system and method according to a fourthembodiment of the present invention; and

FIGS. 10A-10C illustrate a prosthetic graft system and method accordingto a fifth embodiment of the present invention shown in use to connecttwo arteries in an end-to-end manner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description is of the best presently contemplatedmodes of carrying out the invention. This description is not to be takenin a limiting sense, but is made merely for the purpose of illustratinggeneral principles of embodiments of the invention. The scope of theinvention is best defined by the appended claims. In certain instances,detailed descriptions of well-known devices, compositions, components,mechanisms and methods are omitted so as to not obscure the descriptionof the present invention with unnecessary detail.

The present invention provides graft systems and methods for use inconnecting blood vessels with the aorta or other blood vessels. Thegraft systems of the present invention promote optimal anastomosis byproviding support rings, sheets or sleeves that provide an optimaltransition at the anastomotic sites between the graft and the host aortaor vessel. These optimal transitions are created by providing supportfor the weaker connecting vessel at the anastomotic coaptation. Eventhough the drawings and embodiments illustrated herein are described inconnection with CABG applications, the principles, systems and methodsof the present invention can also be applied to other similarapplications, such as in the peripherals (such as the extremities) andfor pulmonary applications.

FIGS. 1A-1C and 2A-2B illustrate a system 20 according to one embodimentof the present invention. The system 20 uses a patient's own vein 22,such as a saphenous vein, as the graft. Referring to FIG. 1A, the vein22 is harvested from the patient using known surgical techniques. Thecollaterals or side branches 24 of the vein 22 are tied off, and thevein 22 can be washed with saline and, optionally, with pharmaceuticalreagents (such as heparin). Then, as shown in FIG. 1B, a first supportring 26 a is slid over the first end 36 of the vein 22, and a secondsupport ring 26 b is slid over the second end 38 of the vein 22. Thesupport rings 26 a, 26 b function to provide support for the weakerconnecting vessel (in this case, the vein 22) at the anastomoticcoaptation, and is described in greater detail below.

Each support ring 26 a, 26 b can be identical in structure, and isillustrated in greater detail using the common designation 26 in FIGS.2A and 2B. The support ring 26 has a generally cylindrical wall 27, andis formed by an oblique cone shaped sleeve having a gradually reducedwall thickness, with the material and wall thickness selected tooptimize the anastomosis that is to be effected. In other words, it isdesired that the wall thickness and material of the support ring 26 beselected so that the support ring 26 can act as a transition thatenables the mechanical properties of the vein graft 22 and the artery oraorta to be anastomosed to be matched as closely as possible.

In particular, the combination of the material and the configuration ofthe support ring 26 at the first end 28 (described below) of the supportring 26 should preferably have features or characteristics similar tothose of an artery so as to facilitate the close matching of themechanical properties or extensibilities. It is believed that such closematching will promote the likelihood of obtaining an optimalanastomosis. In this regard, the material should be sufficiently elasticto allow the support ring 26 at its first end 28 to expand underarterial pressure, just as an artery would, so that the support ring 26would expand along with the artery and vein graft 22 at the site of theanastomosis. In addition, the material should exhibit non-linearexpansion properties. In other words, the material should havesufficient stiffness so that it will not expand beyond a certain limit.Moreover, the material should preferably be nonresorbable or slowlyresorbable in the receiving host by the surrounding tissue in which itis implanted.

Materials that exhibit the above-referenced features or characteristicsinclude synthetic or natural elastomers (e.g., silicone elastomers,silicone rubbers, polyurethanes). Other types of materials that may besuitable include a fiber reinforced composite material containing anelastomeric matrix with a fabric mesh, or a fabric mesh with elastictextile configuration embedded in a flexible non-elastomeric matrix. Itis also possible to use elastic materials with biological originscontaining collagen and elastin network; such as a mammalian artery.

The support ring 26 has opposing first and second ends 28 and 30,respectively, defining first and second openings 32 and 34,respectively. The first opening 32 has a greater diameter than thesecond opening 34, and the thickness of wall 27 is greatest at the firstend 28 and gradually decreases to the smallest thickness at the secondend 30. The decrease in the wall thickness from the first end 28 to thesecond end 30 can be linear, or can be expressed in a more complex form,such as exponential or parabolic. The longitudinal cross-section of thewall 27 may be triangular or shaped as an airfoil or other shapeproviding a smooth transient surface.

The inner diameter of the support ring 26 along its longitudinal lengthis preferably generally consistent throughout, and is slightly largerthan the outer diameter of the vein graft 22 over which it is to bedisposed. When the support ring 26 is placed longitudinally along ahorizontal axis LA, the first end 28 is disposed at an angle A withrespect to the horizontal axis LA. This angle A can be referred to asthe anastomotic surface angle, and preferably ranges from 30 to 90degrees relative to the horizontal axis LA if the first end 28 isintended to be anastomosed to an artery or in a side-to-end manner, asdescribed below. The second end 30 is disposed generally perpendicular(i.e., at about 90 degrees) to the horizontal axis LA.

FIG. 1C illustrates how the graft assembly 20 is used to accomplishbypass grafting between the aorta 40 and a distal coronary artery 42 ofa patient. Referring back to FIG. 1B, the support rings 26 a, 26 b aresecured to the first and second ends 36 and 38, respectively, of thevein 22 by sliding the rings 26 a, 26 b over the ends 36 and 38,respectively, in a manner so that the first larger ends 28 of the rings26 a, 26 b face the ends 36, 38 of the vein 22, and then everting theends 36, 38 over the first ends 28 of the rings 26 a, 26 b and applyinga stitching. As an alternative, the ends 36, 38 of the vein 22 do notneed to be everted, but can be merely stitched to the first ends 28 ofthe rings 26 a, 26 b. The combined first end 28 of the first supportring 26 a and the first end 36 of the vein 22 are anastomosed inside-to-end manner to the aorta 40 by stitches 44. The combined firstend 28 of the second support ring 26 b and the second end 38 of the vein22 are anastomosed in end-to-side manner to the artery 42 by another setof stitches 46. The second ends 30 of the rings 26 do not need to beconnected to the vein 22.

The cross-section of the first opening 32 of the support ring 26 can beeither circular or oval, depending upon the type, location, size andshape of the artery or aorta to be anastomosed. In general, the firstopening 32 is preferably circular in the cases (i) where the supportring 26 is to be anastomosed in a side-to-end manner, at an almostperpendicular orientation, to the aorta or vessel, or (ii) where thesupport ring 26 is to be anastomosed in an end-to-end manner to thevessel. In contrast, the first opening 32 is preferably oval in thecases (i) where the support ring 26 is to be anastomosed in aend-to-side manner, at an angled (but other than perpendicular)orientation, to the aorta (such as 40) or vessel, or (ii) where it isdesired to increase the circumference of the anastomosis (since an ovalhas a greater circumference than a circle), or (iii) where the artery orvessel has a thin profile (i.e., small diameter) which is better suitedto a thinner anastomotic opening provided by an oval configuration, or(iv) for side-to-side anastomosis. Referring back to FIGS. 1A-1C, thefirst opening 32 of the first support ring 26 a can be circular becausethe first opening 32 is generally perpendicular to the aorta 40, andbecause the first support ring 26 a is used in anastomosing a largerartery (such as the aorta 40). The first opening 32 of the secondsupport ring 26 b should be generally oval since it is anastomosed inend-to-side manner to a relatively thin-profile artery 42. In addition,the short axis y or width of the oval opening 32 of the second supportring 26 b is designed to match the shape of the opening of the artery42. The long axis x or height is a function of the ratio x/y, whichrepresents the ratio of the long axis x over the short axis y. Thus, fora circular opening, x and y will be the same. The length L of eachsupport ring 26 can be determined by the ratio L/ID, which is the ratiobetween the length L and the internal diameter ID of the ring 26 at thesecond end 30. If the cross-section of the ring 26 is oval, then theratio is preferably 2L/(x+y). The range of the ratios x/y and 2L/(x+y)can range from 1 to 5. For example, a smaller ratio results in a shorterlength L for the support ring 26, thereby providing a more abrupttransition, and is generally preferred for end-to-end anastomosis, or incircumstances where a shorter support ring 26 is required, such as wherethe vein graft 22 is short. Conversely, a larger ratio results in agreater length L for the support ring 26, thereby providing a moreconsistent and smoother transition, and is generally preferred forside-to-end anastomosis (e.g., at the anastomosis between aorta 40 andthe end 36 of vein graft 22 in FIG. 1C).

Thus, the graft system 20 provides a bypass graft in the form of a vein22 having its opposite, weak, ends 36 and 38 supported by support rings26 a and 26 b, respectively, at the anastomotic sites. The gradualdecreasing thickness of the wall 27 provides the strongest support atthe first and 28, where the wall 27 has the greatest thickness, and alsoprovides a gradually increasing flexibility (i.e., as the thicknessdecreases) from the location of the stitches 44 to the uncovered portionof the vein 22. As a result, the extensibility of the combined first end28 of the support ring 26 and the end 36 or 38 of the vein 22 comesclose to matching the extensibility of the aorta 40 or artery 42 towhich it is to be anastomosed. Similarly, the extensibility of the thinsecond end 30 of the support ring 26 comes close to matching theextensibility of the uncovered portion of the vein 22. As describedabove, the choice of materials for the support rings 26 a, 26 b furtherpromotes this matching of the extensibilities.

In addition, the graft assembly 20 minimizes overstretching, and reducesthe stress concentration, of the wall of the vein graft 22. This isillustrated more clearly in FIGS. 3-4. First, FIG. 3A illustrates aconventional vein graft VG that is anastomosed to an artery AR bystitches S at zero mmHg of pressure (i.e., no arterial blood flow). Whenthis vein graft VG is in use after implantation inside a human body, itwill experience arterial pressure of about 70-140 mmHg. As illustratedin FIG. 3B, this pressure will cause the vein graft VG to bend (see bendlocation SL) to assume a larger diameter LD, thereby increasing thestress concentration of the venous wall of the vein graft VG at the bendlocation SL and creating a blood flow boundary FB separation at the siteof the anastomosis. On the other hand, the smooth transition provided bythe support rings 26 in the graft assembly 20 of the present inventionminimizes the bending and stress concentration of the wall 27 of thevein graft 22, as shown in FIGS. 4A and 4B. In addition, the graduallydecreasing thickness of the wall 27 of the support rings 26 provides asmooth divergent transition which controls most flow boundaryseparations that may be present downstream from the anastomosis sites.

FIGS. 5A-5D and 6A-6B illustrate another system 50 according to thepresent invention, in which a vein graft 52 is used to connect twocoronary arteries in end-to-end manner. The system 50 again uses apatient's own vein 52, such as a saphenous vein, as the graft. Referringto FIG. 5A, the vein 52 is harvested from the patient and prepared inthe same manner as the vein 22 prior to implantation. Then, as shown inFIG. 5B, a first support ring 56 a is slid over the first end 58 of thevein 52, and a second support ring 56 b is slid over the second end 60of the vein 52. The support rings 56 a, 56 b function to provide supportfor the weaker connecting vessel (in this case, the vein 52) at theanastomotic coaptation.

Each support ring 56 a, 56 b may be identical, and is illustrated ingreater detail using the common designation 56 in FIGS. 2A and 2B. Thecharacteristics, materials and features of the support ring 56 areessentially the same as those described above for the support rings 26,except that the wall 57 of the support ring 56 has a tapered conicalstructure, as opposed to the oblique cone shape of the wall 27. Thesupport ring 56 has opposing first and second ends 62 and 64 that definefirst and second openings 66 and 68, respectively. The first opening 66has a greater diameter than the second opening 68, and the thickness ofwall 57 is greatest at the first end 62 and gradually decreases, in agenerally linear manner, to the smallest thickness at the second end 64.The inner diameter of the support ring 56 along its longitudinal lengthis preferably consistent throughout, and is slightly larger than theouter diameter of the vein graft 22 over which it is to be disposed.When the support ring 56 is placed longitudinally along a horizontalaxis LA, the first end 62 and second end 64 are disposed generallyperpendicular with respect to the horizontal axis LA.

FIG. 5D illustrates how the graft system 50 is used to connect twocoronary arteries 70 and 72 in end-to-end manner. Referring back to FIG.5C, the support rings 56 a, 56 b are secured to the first and secondends 58 and 60, respectively, of the vein 52 by sliding the rings 56 a,56 b over the ends 58 and 60, respectively, in a manner so that thefirst larger end 62 of the rings 56 a, 56 b face the outward ends 58, 60of the vein 52. The ends 58, 60 can then be everted over the first ends62 of the rings 56 a, 56 b and stitched, or just merely stitched to theends 62 without any everting. The combined first end 62 of the firstsupport ring 56 a and the first end 58 of the vein 52 are anastomosed toa first coronary artery 70 by stitches 73. The combined first end 62 ofthe second support ring 56 b and the second end 60 of the vein 52 areanastomosed to a second coronary artery 72 by another set of stitches74.

As with the support rings 26, the cross-section of the first opening 66of the support ring 56 can be either circular or oval, with the sameprinciples explained above being applicable as well.

Thus, the graft assembly 50 enjoys the same benefits as the graftassembly 20 described above, in which the opposite, weak, ends 58 and 60of the vein 52 are supported by support rings 56 a and 5 b,respectively, providing an optimal transition at the anastomosis sites.

FIGS. 7A-7C and 8A-8B illustrate another system 80 according to thepresent invention. The system 80 uses a patient's own vein 82, such as asaphenous vein, as the graft for side-to-side anastomosis with anartery. Referring to FIG. 7A, the vein 82 is harvested from the patientand prepared in the same manner as for vein 22. The vein 82 has a sideopening 83 for anastomosis to a side opening in an artery 96. Next, asshown in FIG. 7B, a support sleeve 86 is slid over the vein 82 so that aside opening 90 of the support sleeve 86 is aligned with the opening 83in the vein 82. The support sleeve 86 functions to provide transitionalsupport for the vein 82 and the artery 96 at the anastomosis.

The support sleeve 86 is illustrated in greater detail in FIGS. 8A and8B. FIG. 8A illustrates the sleeve 86 in the form of a rectangular sheet88 having opposite end edges 91 and 93 that can be sutured to form thesleeve 86. When the edges 91 and 93 are sutured, the sleeve 86 has agenerally cylindrical configuration (see FIG. 7B) that is adapted tocorrespond to the configuration and dimension of the vein graft 82. Tofit the vein graft 82 inside the sleeve 86, the width B of the sheet 88should be slightly greater than the circumference of the vein 82 toallow sufficient room for the provision of a suture line 98 thatconnects edges 91 and 93. In addition, the length A of the sheet 88 canbe determined according to a ratio A/B, with the ratio A/B ranging from1 to 10. As with the ratios described above, a smaller ratio means thatthe size of the sleeve 86 is smaller, thereby providing a more abrupttransition, and is generally preferred for situations where thephysiology requires a smaller sleeve, such as where there is abifurcation or bend near the anastomotic site. Conversely, a largerratio results in a larger sleeve 86, thereby providing a more consistentand smoother transition, and is generally preferred for mostapplications.

The sheet 88 has an opening 90 that is adapted to be aligned with theopening 83 of the vein 82. The openings 83 and 90 are preferablyconfigured to match the artery 96 to be anastomosed. In this embodiment,both openings 83 and 90 are illustrated as being oval in configurationbecause (i) it is desired to increase the circumference of the opening,(ii) of the smaller profile of the artery 96, and (iii) the anastomosisis side-to-side. The opening 90 also has a short axis b that is close tothe outer diameter of the artery 96, and a long axis a that can bedetermined according to a ratio a/b, with the ratio a/b ranging from 1to 5. The significance of this ratio a/b and its related principles aresimilar to those for the ratios x/y and 2L/(x+y) described above.Finally, the openings 83 and 90 can assume any shape and size, exceptthat the shapes and sizes should be closely matched.

The sheet 88 has a wall thickness that is greatest at the centralportion at the opening 90, and that gradually decreases in a radialmanner to the edges 91, 92, 93, 94 of the sheet 88 where the wallthickness is the smallest. The gradual reduction in wall thickness ofthe sheet 88 can be linear, or can be expressed in a more complex form,such as exponential or parabolic. The wall thickness and material of thesheet 88 are selected to optimize the anastomosis that is to beeffected. In other words, it is desired that the wall thickness andmaterial of the sheet 88 at the opening 90 be selected so that the sheet88 can act as a transition that enables the extensibilities of the veingraft 82 and the artery to be anastomosed to be matched as closely aspossible. In this regard, the material of the sheet 88 may be same asthose materials described above for the support ring 26.

FIG. 7C illustrates how the graft assembly 80 is used for side-to-sideanastomosis of the vein graft 82 and an artery 96. Referring back toFIG. 7B, the support sleeve 86 is first secured to the vein graft 82 bystitching. During this step, the support sleeve 86 can be provided inthe form of the sheet 88 and then its edges 91 and 93 stitched to formthe sleeve. Alternatively, the support sleeve 86 can be provided in afully assembled generally tubular configuration and slid over the veingraft 82. The aligned openings 90 and 83 are then aligned with a sideopening in the artery 96 and anastomosed by stitches 99. Thus, thesupport sleeve 86 provides support at the anastomosis site, as well as atransition at the anastomosis site between the sides of the vein graft82 and the artery 96 that promotes the matching of the extensibilitiesof the vein graft 82 and the artery 96.

FIG. 9 illustrates a graft system 110 according to a fourth embodimentof the present invention shown in a coronary artery bypass graft system,in which the principles illustrated in FIGS. 1-8 above are utilized in asingle system. The system 110 provides a vein graft 112 that isanastomosed at three locations to an aorta 114 and two arteries 116,118. A support ring 56, such as the support ring 56 of FIGS. 6A and 6B,is secured to a first end of the vein graft 112, which is anastomosed inan side-to-end manner to the aorta 114. A support ring 26, such assupport ring 26 of FIGS. 2A and 2B, is secured to a second end of thevein graft 112, which is anastomosed in an end-to-side manner to anartery 116. A support sleeve 86 is supported at a mid-portion of thevein graft 112, which is anastomosed in a side-to-side manner to anotherartery 118.

FIGS. 10A-10C illustrate another system 130 according to the presentinvention, in which a prosthetic graft 132 is used to connect twoarteries 134, 136 in end-to-end manner. The system 130 provides aprosthetic graft 132, which is preferably made of a non-expandablematerial, such as Dacron or ePTFE (polytetrafluoroethylene). Referringto FIG. 10B, a first support ring 56 a is slid over the anastomotic endof the first artery 134, and a second support ring 56 b is slid over theanastomotic end of the second artery 136. The support rings 56 a, 56 bcan be the same as those described under the designation 56 in FIGS. 6Aand 6B. The support rings 56 a, 56 b are secured to the anastomotic endsof the arteries 134, 136, respectively, by sliding the rings 56 a, 56 bover the ends in a manner so that the first larger end 62 of the rings56 a, 56 b face the anastomotic site (i.e., facing the graft 132) andthen applying a stitching (such as the use of guide stitches). Thecombined first end 62 of the first support ring 56 a and the end of thefirst artery 134 are anastomosed to a first end 138 of the graft 132 bystitches 139. Similarly, the combined first end 62 of the second supportring 56 b and the end of the second artery 136 are anastomosed to asecond end 140 of the graft 132 by stitches 141.

Thus, as with the other embodiments set forth herein, the graft assembly130 provides support rings on the weaker ends of the anastomotic sites.In this case, the weaker ends are the arteries 134, 136, since the graft132 is a prosthetic graft having a structure and material that isstronger or stiffer than the arteries 134, 136. The gradual decreasingthickness of the wall 57 provides the strongest support at the first end62 of the support ring 56, where the wall 57 has the greatest thickness,and also provides a gradually increasing flexibility (i.e., as thethickness decreases) from the location of the stitches 139, 141 to theuncovered portions of the arteries 134, 136, respectively.

Thus, the support rings 26, 56 and the support sleeve 86 that are usedin the graft systems and methods according to the present inventionpromote optimal anastomosis. The support rings 26, 56 and the supportsleeve 86 make it easier for the surgeon to create an optimalanastomosis because they render the graft systems easier to handle andvisualize, they provide external circumferential support to the weakervessel (i.e., either the vein graft or the diseased artery) at theanastomosis site, they provide an effective seal for the anastomosis,and they prevent suture cutting through the vein graft or the diseasedartery, thereby minimizing bleeding. In addition, the graduallydecreasing wall thickness of the support rings 26, 56 and the supportsleeve 86 provides a gradually tapering or withdrawing of the supportfrom the anastomotic coaptation. The support rings 26, 56 and thesupport sleeve 86 further provide proper contour for the vein graft orarteries, and minimize overstrain, stress, and buckling whilemaintaining the continuity of the arterial pulse wave propagation. Asmooth transition of internal stress and interluminal flow boundary isprovided from the anastomotic end (i.e., the thickest end) of thesupport rings 26, 56 and the support sleeve 86 to the other end, therebyminimizing the possibility of flow boundary separation. This smooth andgradual stress and boundary transition is achieved by the geometry(e.g., tapering and decreasing thickness) of the support rings 26, 56and the support sleeve 86, and the property transition of the materialsof the support rings 26, 56 and the support sleeve 86.

While the description above refers to particular embodiments of thepresent invention, it will be understood that many modifications may bemade without departing from the spirit thereof. The accompanying claimsare intended to cover such modifications as would fall within the truescope and spirit of the present invention.

What is claimed is:
 1. A graft system, comprising: a vein graft having aside opening; and a support sleeve having a thickness, a first sideedge, a second side edge, and an opening, the support sleeve surroundingthe vein graft so that the opening of the support sleeve is aligned withthe side opening of the vein graft, with the thickness of the supportsleeve being greater at the opening than at the first and second sideedges.
 2. The graft system of claim 1, wherein the vein graft is a hostsaphenous vein.
 3. The graft system of claim 1, wherein the thickness ofthe support sleeve gradually decreases from the opening of the supportsleeve to the first and second edges thereof.
 4. The graft system ofclaim 3, wherein the thickness of the support sleeve gradually decreasesin a linear manner from the opening of the support sleeve to the firstand second edges thereof.
 5. The graft system of claim 1, wherein thesupport sleeve is provided in the form of a sheet having opposing thirdand fourth edges, and wherein the sheet is wrapped around the vein graftand the third and fourth edges are stitched together.
 6. The graftsystem of claim 1, wherein the support sleeve is made of an elasticmaterial having sufficient stiffness so that it will not expand beyond acertain limit.
 7. A support sleeve for providing side-to-sidetransitional support to the side of either a graft or a host vessel thathas a side opening, the support sleeve having a thickness andcomprising: a first side edge, a second side edge, and an opening, thesupport sleeve surrounding a side opening of a graft or host vessel sothat the opening of the support sleeve is aligned with the side openingof the graft or host vessel, with the thickness of the support sleevebeing greater at the opening than at the first and second side edges. 8.The support sleeve of claim 7, wherein the thickness of the supportsleeve gradually decreases from the opening of the support sleeve to thefirst and second edges thereof.
 9. The support sleeve of claim 8,wherein the thickness of the support sleeve gradually decreases in alinear manner from the opening of the support sleeve to the first andsecond edges thereof.
 10. The support sleeve of claim 7, wherein thesupport sleeve is provided in the form of a sheet having opposing thirdand fourth edges that are stitched together.
 11. The support sleeve ofclaim 7, wherein the support sleeve is made of an elastic materialhaving sufficient stiffness so that it will not expand beyond a certainlimit.